The present invention relates to a monochromatic tone display apparatus for producing a pseudocolor display by using a monochromatic display device.
A monochromatic tone system is defined as a system for producing a pseudocolor display by using a monochromatic display. Tone levels are determined in correspondence with respective colors, and tone differences are expressed on the monochromatic display by utilizing tone level differences. For example, one-bit I (intensity) data is added to the 3-bit data of R.multidot.G.multidot.B to represent 8 colors and to format the 4-bit data of I.multidot.R.multidot.G.multidot.B which can express 16 tones corresponding to 16 colors. When the 4-bit data is displayed on the monochromatic display, the 4-bit data can display a maximum of 16 tones. In other words, 16 tone levels are given in correspondence with 16 colors. The I bit is set at logic "0" in the normal mode, and at logic "1" in an emphasizing mode.
A typical example is described in "IBM Personal Computer XT Hardware Reference Library Technical Reference". However, this reference describes only interface color graphic specifications. No description is made of a compression tone display which serves as the main feature of the present invention.
Assume that the 4-bit data of I.multidot.R.multidot.G.multidot.B is weighted to provide a color code C=I.times.8+R.times.4+G.times.2+B, and that numbers 0 through 15 are given by Cs, respectively, as shown in FIG. 1. The smaller the color code, the lower the tone level. The larger the color code, the higher the tone level.
According to the above-described system, however, since the difference between the adjacent tone levels is small, the difference cannot be easily identified. In addition, since the I bit among the I, R, G and B bits has the maximum weight coefficient, the screen is darkened when the I bit is enabled.